As device sizes continue to shrink, the critical dimensions of photolithographic features also must shrink. Common photolithographic patterning of small geometries, however, is increasingly difficult, especially in trench structures, to the point that photolithographic masking techniques may no longer be efficient or even capable of producing desired small geometries (e.g., less than 10 nanometers (nm)). A variety of techniques have been suggested, such as reflowing the patterned photoresist mask, or using light having a carefully selected wavelength, to create a desirably small pattern on the mask.
Another technique is to use a self-aligned etch technique (i.e. no photomask) using a deposited polymer layer 1 to pattern and shrink the size of the underlay that is exposed to the etchant gas. The problem with this technique is that it can result in undesirable etching damage to the top side and corners of the layer or layers underlying the polymer layer during subsequent etching steps. FIG. 1 illustrates typical etching results that can occur, which include etching off the top surface 2 and rounding of the corners 4, 6 of the layer to be etched 8. This problem becomes more acute as trench sizes shrink
Since conventional techniques are unable to protect the top side and corners of etched layer from damage during subsequent etching processes it would be desirable to provide a self-aligned etch technique (i.e., one that uses no photoresist mask) that enables the formation of small critical-dimension etched features while minimizing or eliminating unwanted damage to upper surfaces and corners of device features. The desired technique should be achievable in a single process chamber to reduce costs.